This chapter covers three theories essential to our understanding of health behavior: Theory of Reasoned Action (TRA), Theory of Planned Behavior (TPB), and Integrated Behavioral Model (IBM). To better guide the appropriate use and application of these theories, it's important to understand the history and development, similarities and differences of each.

Theory of Reasoned Action

TRA was first introduced in 1967 by Fishbein; it asserts that the most important determinant of a person's behavior is a person's behavioral intention (comprised of attitude and subjective norms associated with the behavior). In contrast to previous theories, Fishbein distinguishes between attitude toward an object (e.g. breast cancer) and attitude toward a behavior (e.g. mammogram screening) with respect to that object.

Theory of Planned Behavior

Later, it was understood that TRA's accuracy in explaining behavior depended on the degree to which the behavior was under volitional control (that is, the degree to which an individual can exercise control over the behavior). Therefore, Ajzen and colleagues proposed TPB as an extension to TRA's framework. TPB is meant to predict behaviors in which people have incomplete volitional control. This extension, perceived behavioral control, is an effort to account for factors outside of the individual's control that may affect the individual's intention or behavior.

Integrated Behavioral Model

The constructs in TRA, TPB and other commonly used health behavior theories (e.g. Health Belief Model, Social Cognitive Theory, and Transtheoretical Model) use many of the same constructs. Despite the similarities of constructs across theories, there has been little effort to integrate them until the early 2000s. The IBM (also known as Integrative Model of Behavioral Prediction) is a general theory of behavioral prediction that is assumed to be applicable to the understanding of any given behavior. Similar to TRA and TPB, the IBM proposes that intentions (as the function of attitudes, subjective norms, and perceived self-efficacy) are the primary determinant of behavior. Four additional components directly affect behavior: knowledge, salience of the behavior, environmental constraints, and habit.

History & Development

Primary Determinant of Behavior

Theory of Reasoned Action (TRA)

Reasoned Action (TRA) Developed by Fishbein in 1969 in effort to provide better understanding of how attitudes impact behavior

Intention

Attitude

Subjective Norms

Theory of Planned Behavior (TPB)

Planned Behavior (TPB) Later, developed by Ajzen and colleagues in late 1980s to address lack of volitional control factor in TRA

Intention

Attitude

Subjective Norms

Perceived Control

Integrated Behavioral Model (IBM)

A culmination of factors led to the development of an integrated model in the early 2000s. Several individuals and organizations had called for consideration of the similarities and differences in commonly used health behavior theories to identify a critical set of variables that may serve as key determinants of behavior (Fishbein et al 1992: NIMH sponsored workshop, IOM 2002)